Little is known about older adult language learners and effects of aging on L2 learning. This study investigated learning in older age through interactions of learner-internal and -external variables; specifically, late-learned L2 (bilingualism) and provision of grammar explanation (explicit instruction, EI). Forty-three older adults (age 60+) who were monolingual English or bilingual English/Spanish speakers learned basic Latin morphosyntax using a computer program with or without EI. Results showed no overall effects of EI, although bilinguals with EI had advantages when transferring skills. Bilinguals also outperformed monolinguals on interpretation regardless of instruction. This study expands the scope of SLA research to include older adults and bilinguals, when traditionally participants are young adult monolinguals. It bolsters nascent research on older adults by adopting a tried-and-true paradigm: interactions between variables. Older adults' overall success at learning language counters negative stereotypes of aging and demonstrates that bilingual linguistic advantages are lifelong.